CN114864922B - Lithium ion battery - Google Patents

Lithium ion battery Download PDF

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Publication number
CN114864922B
CN114864922B CN202210466861.3A CN202210466861A CN114864922B CN 114864922 B CN114864922 B CN 114864922B CN 202210466861 A CN202210466861 A CN 202210466861A CN 114864922 B CN114864922 B CN 114864922B
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positive electrode
phosphate
compound
ether
ion battery
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CN114864922A (en
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钱韫娴
邓永红
李红梅
胡时光
向晓霞
皮琛琦
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Shenzhen Capchem Technology Co Ltd
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Shenzhen Capchem Technology Co Ltd
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Priority to PCT/CN2023/080934 priority patent/WO2023207369A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

In order to solve the problem that the cycle performance is reduced due to manganese ion dissolution and electrolyte decomposition of the existing lithium nickel manganese oxide battery, the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, and the positive electrode material layer comprises a lithium nickel manganese oxide material shown in a formula I and a compound shown in a formula II; liNi x Mn 2‑x O 4 Formula I, wherein 0 < x < 2;the nonaqueous electrolyte includes a nonaqueous organic solvent, an electrolyte salt, and a first additive including a boron-containing lithium salt; the lithium ion battery meets the following conditions: m is less than or equal to 0.1 and less than or equal to 5; and a is more than or equal to 0.005 and less than or equal to 1, b is more than or equal to 0.01 and less than or equal to 3, and m is more than or equal to 1 and less than or equal to 3. The lithium ion battery provided by the invention can maintain the structural stability and oxidation resistance of high-voltage lithium nickel manganese oxide under the condition of higher energy density, and remarkably inhibit the decomposition reaction of electrolyte, so that the cycle performance of the battery is improved.

Description

Lithium ion battery
Technical Field
The invention belongs to the technical field of energy storage electronic parts, and particularly relates to a lithium ion battery.
Background
Lithium Ion Batteries (LIBs) have the advantages of high working voltage, small self-discharge, long cycle life, no memory effect, environmental friendliness, good safety performance and the like, and are dominant in the markets of portable electronic equipment and electric automobiles, so that the lithium ion batteries need to develop towards a higher energy density in order to meet the long-term development requirement. The energy density is largely dependent on the product of the specific capacity of the positive electrode and the operating voltage, and therefore, development and application of high-voltage materials are imperative.
High-voltage spinel lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4 The (LNMO) positive electrode has the advantages of high operating voltage, low cost, environmental friendliness and the like, and is attracting more and more attention. Although spinel structured LiNi 0.5 Mn 1.5 O 4 The working voltage is higher than 4.7V (vs. Li/Li+), however, the Jahn-Teller effect can cause dissolution of manganese ions in the crystal lattice when the crystal lattice is cycled under high voltage, so that the specific discharge capacity of the battery is quickly attenuated, meanwhile, the electrolytic solution is oxidized and decomposed under the high voltage working condition, and the reaction product of the decomposition product and the electrode material is accumulated on the surface of the particles to prevent normal deintercalation of Li < + >, so that the method becomes a bottleneck for restricting commercial application of the lithium ion battery. Conventional organic carbonates and LiPF 6 The combined oxidative decomposition potential (relative to li+/Li) is about 4.5V, and is easily oxidized and decomposed at high voltage, and the generated by-products further affect the formation of effective SEI interface film, resulting in poor cycle stability.
Aiming at the problems of LNMO, at present, a film forming additive is usually introduced into electrolyte to passivate the surface of a positive electrode material, the side reaction is reduced, the cycle performance is improved, and functional additives such as overcharge prevention, flame retardance and the like are introduced to improve the safety performance. However, by introducing a film forming additive and an overcharge preventing and flame retarding functional additive into the electrolyte, the lithium ion battery has difficulty in achieving comprehensive properties such as impedance, circulation, safety and the like.
Disclosure of Invention
Aiming at the problem of the reduction of the cycle performance caused by the dissolution of manganese ions and the decomposition of electrolyte in the existing lithium nickel manganese oxide battery, the invention provides a lithium ion battery.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and nonaqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, and the positive electrode material layer comprises a lithium nickel manganese oxide material shown in a formula I and a compound shown in a formula II;
LiNi x Mn 2-x O 4 i is a kind of
Wherein x is more than 0 and less than 2;
wherein R is 1 、R 2 、R 3 Each independently selected from alkyl of 1 to 5 carbon atoms, fluoroalkyl of 1 to 5 carbon atoms, ether of 1 to 5 carbon atoms, fluoroether of 1 to 5 carbon atoms, unsaturated hydrocarbon of 2 to 5 carbon atoms, and R 1 、R 2 、R 3 At least one of which is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;
the nonaqueous electrolyte includes a nonaqueous organic solvent, an electrolyte salt, and a first additive including a boron-containing lithium salt;
the lithium ion battery meets the following conditions:
0.1≤(a+b)*m≤5；
and a is more than or equal to 0.005 and less than or equal to 1, b is more than or equal to 0.01 and less than or equal to 3, and m is more than or equal to 1 and less than or equal to 3;
wherein a is the mass percentage of the compound shown in the formula II in the positive electrode material layer, and the unit is;
b is the mass percentage content of boron-containing lithium salt in the nonaqueous electrolyte, and the unit is;
m is the capacitance of the positive electrode material layer per unit area, and the unit is mAh/cm 2 。
Optionally, the lithium ion battery meets the following conditions:
0.5≤(a+b)*m≤2。
optionally, the mass percentage content a of the compound shown in the formula II in the positive electrode material layer is 0.05% -0.3%.
Optionally, the mass percentage content b of the boron-containing lithium salt in the nonaqueous electrolyte is 0.05% -1%.
Optionally, the capacitance m of the unit area of the positive electrode material layer is 1.6-2.5 mAh/cm 2 。
Optionally, the lithium nickel manganese oxide material shown in formula I is selected from LiNi 0.1 Mn 1.9 O 4 、LiNi 0.2 Mn 1.8 O 4 、LiNi 0.5 Mn 1.5 O 4 、LiNi 0.8 Mn 1.2 O 4 、LiNi 1.0 Mn 1.0 O 4 、LiNi 1.2 Mn 0.8 O 4 、LiNi 1.5 Mn 0.5 O 4 Or LiNi 1.8 Mn 0.2 O 4 At least one of (a) and (b);
preferably, the mass percentage of the lithium nickel manganese oxide material shown in the formula I in the positive electrode material layer is 90.0% -99%.
Optionally, the solution obtained after ultrasonic oscillation of the positive electrode in the solvent is analyzed by a liquid chromatography-mass spectrometer (LC-MS), and characteristic peaks appear in a region with retention time of 6.5-7.5 min.
Optionally, the boron-containing lithium salt is selected from one or more of lithium bisoxalato borate, lithium difluorooxalato borate and lithium tetrafluoroborate.
Alternatively, the alkyl group of 1 to 5 carbon atoms is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl or neopentyl; a fluoroalkyl group having 1 to 5 carbon atoms selected from the group consisting of a group in which one or more hydrogen elements in the alkyl group having 1 to 5 carbon atoms are substituted with a fluorine element;
The unsaturated hydrocarbon group of 2 to 5 carbon atoms is selected from vinyl, propenyl, allyl, butenyl, pentenyl, methylvinyl, methallyl, ethynyl, propynyl, propargyl, butynyl or pentynyl;
the ether group with 1-5 carbon atoms is selected from methyl ether, diethyl ether, methylethyl ether, propyl ether, methylpropyl ether or ethylpropyl ether;
the fluoroether group with 1-5 carbon atoms is selected from fluoromethyl ether, fluoroethyl ether, fluoromethyl ethyl ether, fluoropropyl ether, fluoromethyl propyl ether or fluoroethyl propyl ether.
Optionally, the compound shown in formula II is selected from at least one of tripropylethyl phosphate, dipropylethyl fluoro methyl phosphate, dipropylethyl methoxy methyl phosphate, dipropylethyl phosphate, trifluoromethyl dipropylethyl phosphate, dipropylethyl 2, 2-trifluoroethyl phosphate, dipropylethyl 3, 3-trifluoropropyl phosphate, hexafluoroisopropyl dipropylethyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, dipropylethyl ether phosphate, dipropylethyl fluoro methyl ether phosphate, 2-trifluoroethyldiallyl phosphate, diallyl 3, 3-trifluoropropyl phosphate or diallyl hexafluoroisopropyl phosphate.
Optionally, the nonaqueous electrolyte further comprises a second additive, and the second additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, an unsaturated phosphate compound, a borate compound and a nitrile compound;
preferably, the second additive is added in an amount of 0.01% to 30% based on 100% of the total mass of the nonaqueous electrolytic solution.
Preferably, the nonaqueous electrolyte further comprises a second additive, and the second additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, an unsaturated phosphate compound, a borate compound and a nitrile compound;
preferably, the addition amount of the second additive is 0.01% -30% based on 100% of the total mass of the nonaqueous electrolyte;
preferably, the cyclic sulfate compound is selected from the group consisting of vinyl sulfate, vinyl 4-methylsulfate, propylene sulfate, vinyl methylsulfate, At least one of (a) and (b);
the sultone compound is selected from 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propylene sultone or At least one of (a) and (b);
the cyclic carbonate compound is at least one selected from ethylene carbonate, fluoroethylene carbonate or a compound shown in a structural formula III,
in the structural formula III, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group;
the unsaturated phosphate compound is at least one compound shown in a structural formula IV:
in the formula IV, R 31 、R 32 、R 33 Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si (C) m H 2m+1 ) 3 M is a natural number of 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group;
the borate compound is at least one selected from tri (trimethylsilane) borate and tri (triethylsilane) borate;
the nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether, hexanedinitrile, adiponitrile, pimelic dinitrile, suberonitrile, nonyldinitrile and decyldinitrile.
According to the lithium ion battery provided by the invention, the nickel lithium manganate material is adopted as the positive electrode active material, meanwhile, the compound shown in the formula II is doped in the positive electrode material layer, and the boron-containing lithium salt is added in the non-aqueous electrolyte as the first additive, through a great deal of researches, the inventor finds that the mass percent a of the compound shown in the formula II in the positive electrode material layer, the mass percent b of the boron-containing lithium salt in the non-aqueous electrolyte and the capacitance m of the positive electrode material layer have a mutual correlation effect, and when the three compounds shown in the formula II, the boron-containing lithium salt in the electrolyte and the high-voltage nickel lithium manganate and the positive electrode material layer meet the limit of 0.1-5, the structural stability and oxidation resistance of the high-voltage nickel lithium manganate material can be kept under the condition of higher energy density, the decomposition reaction of the electrolyte is obviously inhibited, and the cycle performance of the battery is improved.
Drawings
Fig. 1 is a graph of a positive electrode sheet obtained by testing a liquid chromatograph-mass spectrometer (LC-MS).
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects solved by the invention more clear, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The embodiment of the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode and nonaqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, and the positive electrode material layer comprises a lithium nickel manganese oxide material shown in a formula I and a compound shown in a formula II;
LiNi x Mn 2-x O 4 i is a kind of
Wherein x is more than 0 and less than 2;
wherein R is 1 、R 2 、R 3 Each independently selected from the group consisting of alkyl groups of 1 to 5 carbon atoms, fluoroalkyl groups of 1 to 5 carbon atoms, ether groups of 1 to 5 carbon atoms, fluoroether groups of 1 to 5 carbon atoms, unsaturated hydrocarbons of 2 to 5 carbon atomsAnd R is a radical 1 、R 2 、R 3 At least one of which is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;
the nonaqueous electrolyte includes a nonaqueous organic solvent, an electrolyte salt, and a first additive including a boron-containing lithium salt;
The lithium ion battery meets the following conditions:
0.1≤(a+b)*m≤5；
and a is more than or equal to 0.005 and less than or equal to 1, b is more than or equal to 0.01 and less than or equal to 3, and m is more than or equal to 1 and less than or equal to 3;
wherein a is the mass percentage of the compound shown in the formula II in the positive electrode material layer, and the unit is;
b is the mass percentage content of boron-containing lithium salt in the nonaqueous electrolyte, and the unit is;
m is the capacitance of the positive electrode material layer per unit area, and the unit is mAh/cm 2 。
The compound shown in the formula II can form a layer of polymer film with good chemical stability, electrochemical stability and thermal stability on the surface of the lithium nickel manganese oxide material in situ; meanwhile, when the boron-containing lithium salt is added into the electrolyte as a first additive, the boron-containing lithium salt is easily oxidized on the surface of the positive electrode to generate inorganic electrolyte salt containing characteristic elements such as boron, the interface film formed by the compound shown in the formula II on the surface of the positive electrode is modified, and the boron element in the inorganic electrolyte salt can be combined with lone pair electrons on oxygen in the positive electrode active material due to vacancy orbitals, so that the oxidation activity of the positive electrode active material is further reduced, the Jahn-Teller effect of the lithium nickel manganese oxide material in high-voltage circulation is inhibited, the dissolution of manganese ions is reduced, and meanwhile, the formed interface film can be better used as an isolating layer of the positive electrode material layer and the nonaqueous electrolyte, the oxidative decomposition of the nonaqueous electrolyte is reduced, the gas expansion and the rapid capacity decay in the high-voltage lithium nickel manganese oxide battery circulation and the storage process are further obviously inhibited, and the manganese ion dissolution and the circulation performance of the lithium nickel manganese oxide battery are synergistically improved.
The inventor finds that in the aspects of inhibiting the dissolution of manganese ions in the positive electrode active material and the decomposition of the nonaqueous electrolyte, the mass percent a of the compound shown in the formula II in the positive electrode material layer, the mass percent b of the boron-containing lithium salt in the nonaqueous electrolyte and the capacitance m of the unit area of the positive electrode material layer have the mutual correlation, and when the three satisfy the condition that the (a+b) m is less than or equal to 5, the synergistic effect between the compound shown in the formula II, the boron-containing lithium salt in the electrolyte, the high-voltage lithium nickel manganese oxide and the capacitance of the positive electrode material layer can be fully exerted, so that the battery can maintain the structural stability and the oxidation resistance of the high-voltage lithium nickel manganese oxide under the condition of higher energy density, the decomposition reaction of the electrolyte is obviously inhibited, and the cycle performance of the battery is improved.
In a preferred embodiment, the lithium ion battery satisfies the following conditions:
0.5≤(a+b)*m≤2。
when the mass percentage content a of the compound shown in the formula II in the positive electrode material layer, the mass percentage content b of the boron-containing lithium salt in the nonaqueous electrolyte and the capacitance m of the unit area of the positive electrode material layer meet the conditions, the dissolution of manganese ions and the decomposition of the electrolyte can be further inhibited, and the cycle performance of the battery can be improved.
In specific embodiments, the mass percentage of the compound represented by formula II in the positive electrode material layer a may be 0.005%, 0.008%, 0.01%, 0.02%, 0.04%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95% or 1%.
In a preferred embodiment, the mass percentage content a of the compound shown in the formula II in the positive electrode material layer is 0.05-0.3%.
When the compound shown in the formula II is used as an electrolyte additive, films can be formed on the surfaces of the positive electrode and the negative electrode at the same time, so that the internal resistance of the battery is increased. In order to solve the problem, the compound shown in the formula II is added into the positive electrode material layer, the interfacial film formed on the surface of the lithium nickel manganese oxide material by the compound shown in the formula II can effectively inhibit electrochemical oxidation reaction between electrolyte and the lithium nickel manganese oxide material, greatly reduce oxygen release of the lithium nickel manganese oxide material, improve oxidation resistance and structural stability of the active material, and meanwhile, the safety performance can be improved due to the fact that the compound shown in the formula II has phosphorus-containing functional groups. Therefore, the compound shown in the formula II is used as the positive electrode slurry additive, so that on one hand, the passivation effect of the compound on the lithium nickel manganese oxide material can be maintained, the oxidation resistance and the structural stability of the positive electrode are improved, the electrochemical performance and the safety performance of the lithium ion battery are further improved, and on the other hand, the problem that the internal resistance of the battery is increased due to the fact that film forming reaction occurs at the positive electrode and the negative electrode simultaneously when the compound is used as the electrolyte additive in the prior art can be solved.
In the positive electrode material layer, if the content of the compound shown in the formula II is too small, the passivation effect on the positive electrode material is limited, so that the improvement effect on the battery performance is not obvious; if the content of the compound represented by formula II is too large, a film is formed too thick on the surface of the positive electrode active material, which increases the internal resistance of the battery.
In a specific embodiment, the mass percentage b of the boron-containing lithium salt in the nonaqueous electrolytic solution is 0.01%, 0.02%, 0.04%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.6%, 1.65%, 1.7%, 1.75%, 1.8%, 1.85%, 1.9%, 1.95%, 2%, 2.1%, 2.15%, 2.2%, 2.25%, 2.3%, 2.35%, 2.4%, 2.45%, 2.5%, 2.55%, 2.6%, 2.65%, 2.7%, 2.75%, 2.95%, 2.3%, 2.95%, or 2.3.95%.
In some embodiments, the mass percentage content b of the boron-containing lithium salt in the nonaqueous electrolyte is 0.05% -1%.
The non-aqueous electrolyte contains boron-containing lithium salt which is used for forming a film on a positive electrode material layer together with the compound shown in the formula II, and is different in that the compound shown in the formula II is doped in the positive electrode material layer, the boron-containing lithium salt is dispersed in the non-aqueous electrolyte, a decomposition product of the boron-containing lithium salt has a modification effect on an interface film obtained by decomposing the compound shown in the formula II, and the two are matched to obtain a novel positive electrode material layer interface film form, and when the mass percentage of the boron-containing lithium salt in the non-aqueous electrolyte is too low, the modification effect on the interface film is not obvious; when the mass percentage of the boron-containing lithium salt in the nonaqueous electrolyte is too high, the film forming reaction on the surface of the positive electrode material layer is stronger, so that the formed interface film is too thick, the impedance of the battery is increased, and the addition amount of other lithium salts, such as lithium hexafluorophosphate, is correspondingly limited, so that the conductivity of the nonaqueous electrolyte is not improved.
In a specific embodiment, the capacitance m of the positive electrode material layer per unit area can be 1.0mAh/cm 2 、1.2mAh/cm 2 、1.5mAh/cm 2 、1.8mAh/cm 2 、2.0mAh/cm 2 、2.2mAh/cm 2 、2.5mAh/cm 2 、2.8mAh/cm 2 Or 3.0mAh/cm 2 。
In a preferred embodiment, the capacitance m of the positive electrode material layer per unit area is 1.6-2.5 mAh/cm 2 。
m represents the capacitance per unit area of the positive electrode material layer, that is, the total amount of active ions releasable per unit area of the positive electrode material layer when the battery is fully discharged, and is related to the positive electrode active material selection, the positive electrode active material content, the compaction density and the coating thickness of the positive electrode material layer. The design capacity of the battery is the same, and under the discharge of the same multiplying power, if the capacitance of the unit area of the positive electrode material layer used by the battery core is larger, the number of active ions which are instantaneously separated from the unit area of the surface of the positive electrode material layer is larger, and the cycle performance of the battery is poorer; however, the larger the capacitance per unit area of the positive electrode material layer, the more active ions can be removed from the positive electrode by the positive electrode material layer representing a smaller area, and the higher the energy density of the battery; conversely, the smaller the battery energy density, the less advantageous the commercial application.
The capacitance m per unit area of the positive electrode material layer can be measured as follows:
step 1): and testing the average discharge capacity of the positive electrode material layer.
And taking the positive electrode, and obtaining a small wafer of the positive electrode material layer by using a punching die. The metal lithium sheet is used as a counter electrode, the Celgard film is used as a separation film, and the LiPF is dissolved 6 (1 mol/L) EC+EMC+The solution of DEC (ethylene carbonate, ethylmethyl carbonate, diethyl carbonate in a volume ratio of 1:1:1) was used as electrolyte, and 5 identical CR2430 button cells were assembled in an argon-protected glove box. And standing for 12h after the battery is assembled, performing constant current charging at a charging current of 0.1C until the voltage reaches an upper limit cutoff voltage of 4.95V, performing constant current discharging at a discharging current of 0.1C until the voltage reaches a lower limit cutoff voltage of 3.4V, and recording the discharge capacity of the first cycle. The average value of the discharge capacity of the 5 button cells is the average discharge capacity of the positive electrode active layer.
Step 2): and (3) taking the average discharge capacity of the positive electrode material layer measured by the average discharge capacity test method of the positive electrode material layer in the step (1). The diameter d of the positive and minimum wafer of the button cell was measured using a caliper and then according to the formula pi (0.5 d) 2 And calculating to obtain the area of the button cell positive and minimum wafer.
Step 3): according to the capacitance m of the unit area of the positive electrode material layer=the average discharge capacity (mAh) of the positive electrode material layer/the area (cm) of the positive electrode small wafer 2 ) And calculating the capacitance m of the positive electrode material layer in unit area.
In some embodiments, the lithium nickel manganese oxide material of formula I is selected from LiNi 0.1 Mn 1.9 O 4 、LiNi 0.2 Mn 1.8 O 4 、LiNi 0.5 Mn 1.5 O 4 、LiNi 0.8 Mn 1.2 O 4 、LiNi 1.0 Mn 1.0 O 4 、LiNi 1.2 Mn 0.8 O 4 、LiNi 1.5 Mn 0.5 O 4 Or LiNi 1.8 Mn 0.2 O 4 But are not limited to, the recited materials, and other non-recited values within the x-value range are equally applicable.
In a preferred embodiment, the lithium nickel manganese oxide material of formula I is selected from the group consisting of LiNi 0.5 Mn 1.5 O 4 。
In a preferred embodiment, the mass percentage of the lithium nickel manganese oxide material shown in the formula I in the positive electrode material layer is 90.0% -99%.
In some embodiments, the solution obtained after the ultrasonic oscillation of the positive electrode in the solvent is analyzed by a liquid chromatography-mass spectrometer (LC-MS), and characteristic peaks appear in a region with a retention time of 6.5 min-7.5 min.
The method for carrying out liquid chromatography-mass spectrometer chromatography analysis on the positive plate comprises the following steps: the battery is disassembled in a glove box to take out the positive electrode, the cut positive electrode is immersed in a proper solvent (such as DMC and acetonitrile) for a proper time through ultrasonic vibration, so that substances in a positive electrode material layer of the positive electrode plate are dissolved in the solvent, then the solution is detected by a liquid chromatography-mass spectrometer (LC-MS), a region with the retention time of 6.5 min-7.5 min has characteristic peaks, as shown in figure 1, wherein the model of the liquid chromatography-mass spectrometer is Waters ACQUITY UPLC/Xex G2-XS qtofMS, and the chromatographic conditions are as follows: using Waters T3 type chromatographic column with column temperature of 35-40deg.C, mobile phase of 40% water and 60% acetonitrile mixture, and mobile phase flow rate of 0.2-0.3ml/min.
In some embodiments, the positive electrode is sonicated in the solvent for a period of 2 hours and more.
In some embodiments, the boron-containing lithium salt is selected from one or more of lithium bisoxalato borate, lithium difluorooxalato borate, and lithium tetrafluoroborate.
Compared with other boron-containing lithium salts, when the boron-containing lithium salt is adopted, oxalic acid boric acid functional groups or fluoro boric acid groups are carried by the boron-containing lithium salt, so that the boron-containing lithium salt is easier to oxidize and decompose on the surface of the positive electrode, and inorganic electrolyte salt with B element is generated, thereby being beneficial to improving the performance of the interfacial film.
In the present invention, the alkyl group of 1 to 5 carbon atoms may be selected from, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl or neopentyl; the fluoroalkyl group having 1 to 5 carbon atoms is selected from the group consisting of a group in which one or more hydrogen elements in the alkyl group having 1 to 5 carbon atoms are substituted with a fluorine element.
The unsaturated hydrocarbon groups of 2 to 5 carbon atoms may be selected from, for example, ethenyl, propenyl, allyl, butenyl, pentenyl, methylvinyl, methallyl, ethynyl, propynyl, propargyl, butynyl, pentynyl.
The ether group of 1 to 5 carbon atoms may be selected from, for example, methyl ether, ethyl ether, methyl ethyl ether, propyl ether, methyl propyl ether, ethyl propyl ether.
The fluoroether group of 1 to 5 carbon atoms may be selected from, for example, fluoromethyl ether, fluoroethyl ether, fluoromethyl ethyl ether, fluoropropyl ether, fluoromethyl propyl ether, fluoroethyl propyl ether.
In a preferred embodiment, the compound of formula II is selected from at least one of tripropylethyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, dipropargyl methoxy methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2, 2-trifluoroethyl phosphate, dipropargyl 3, 3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, dipropargyl methyl ether phosphate, dipropargyl fluoro methyl ether phosphate, 2-trifluoroethyl diallyl phosphate, diallyl 3, 3-trifluoropropyl phosphate or diallyl hexafluoroisopropyl phosphate.
In a preferred embodiment, the compound of formula II is selected from one or more of the following compounds:
the compound shown in the formula II can form an effective interfacial film on the surface of the lithium nickel manganese oxide material in situ, so that the battery has the properties of low impedance, circulation, safety and the like.
In some embodiments, the positive electrode material layer further comprises a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the compound shown in formula II, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.
The mass percentage of the positive electrode binder is 1-2% and the mass percentage of the positive electrode conductive agent is 0.5-2% based on 100% of the total mass of the positive electrode material layer.
The positive electrode binder includes thermoplastic resins such as polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, polypropylene, and the like; an acrylic resin; sodium hydroxymethyl cellulose; polyvinyl butyral; ethylene-vinyl acetate copolymers; polyvinyl alcohol; and one or more of styrene butadiene rubber.
The positive electrode conductive agent comprises one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.
In some embodiments, the compound of formula II is formed on the surface of the positive electrode material layer, or the compound of formula II is incorporated inside the positive electrode material layer.
When the compound represented by the formula II is formed on the surface of the positive electrode material layer, the preparation method thereof may be referred to as follows:
and forming a coating containing the compound shown in the formula II on the surface of the positive electrode material layer by a surface coating mode, specifically, dispersing a positive electrode active material, a positive electrode conductive agent and a positive electrode binder in an organic solvent to prepare positive electrode slurry, coating and drying the positive electrode slurry to form the positive electrode material layer, dispersing the compound shown in the formula II in the organic solvent, spraying the obtained compound solution shown in the formula II on the surface of the positive electrode material layer, and drying to remove the solvent to obtain the positive electrode material layer containing the compound shown in the formula II.
When the compound represented by the formula II is blended in the inside of the positive electrode material layer, the preparation method thereof can be referred to as follows:
The first mode is that the positive electrode slurry for preparing the positive electrode material layer contains a compound shown in a formula II, specifically, the compound shown in the formula II, a positive electrode active material, a positive electrode conductive agent and a positive electrode binder can be dispersed in an organic solvent to prepare positive electrode slurry, and then the positive electrode slurry is coated and dried to form the positive electrode material layer;
and secondly, preparing a positive electrode material layer, soaking the positive electrode material layer in a solution containing a compound shown in a formula II, enabling the compound shown in the formula II to permeate into the positive electrode material layer, and drying and removing the solvent to obtain the positive electrode material layer containing the compound shown in the formula II.
In some embodiments, the positive electrode further comprises a positive electrode current collector, and the positive electrode material layer is formed on a surface of the positive electrode current collector.
The positive current collector is selected from a metal material that can conduct electrons, preferably, the positive current collector includes one or more of Al, ni, tin, copper, stainless steel, and in a more preferred embodiment, the positive current collector is selected from aluminum foil.
In some embodiments, the nonaqueous organic solvent includes one or more of an ether solvent, a nitrile solvent, a carbonate solvent, and a carboxylate solvent.
In some embodiments, the ether solvent includes cyclic or chain ethers, preferably chain ethers of 3 to 10 carbon atoms and cyclic ethers of 3 to 6 carbon atoms, which may be specifically but not limited to 1, 3-Dioxolane (DOL), 1, 4-Dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH) 3 -THF), 2-trifluoromethyl tetrahydrofuran (2-CF) 3 -THF) one or more of; the chain ether may be, but not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether. The solvation capability of the chain ether and lithium ions is high, so that the ionic decomposition can be improvedSince the ionic property is particularly preferable, dimethoxymethane, diethoxymethane and ethoxymethoxymethane which have low viscosity and can impart high ionic conductivity are particularly preferable. The ether compound may be used alone, or two or more of them may be used in any combination and ratio. The amount of the ether compound to be added is not particularly limited, and is arbitrary within a range that does not significantly impair the effect of the highly compacted lithium ion battery of the present invention, and is usually 1% or more, preferably 2% or more, more preferably 3% or more in terms of the volume ratio of the nonaqueous solvent of 100%, and is usually 30% or less, preferably 25% or less, more preferably 20% or less in terms of the volume ratio. When two or more ether compounds are used in combination, the total amount of the ether compounds may be set to satisfy the above range. When the amount of the ether compound is within the above preferred range, the effect of improving the ionic conductivity due to the increase in the dissociation degree of lithium ions and the decrease in the viscosity of the chain ether can be easily ensured. In addition, when the negative electrode active material is a carbon material, co-intercalation of the chain ether and lithium ions can be suppressed, and thus the input/output characteristics and the charge/discharge rate characteristics can be brought into appropriate ranges.
In some embodiments, the nitrile solvent may be, but is not limited to, one or more of acetonitrile, glutaronitrile, malononitrile.
In some embodiments, the carbonate-based solvent includes a cyclic carbonate or a chain carbonate, which may be specifically but not limited to one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), gamma-butyrolactone (GBL), butylene Carbonate (BC); the chain carbonate may be, but is not limited to, in particular, one or more of dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited, and is arbitrary within a range that does not significantly impair the effect of the lithium ion battery of the present invention, but in the case of using one of them alone, the lower limit of the content is usually 3% by volume or more, preferably 5% by volume or more, relative to the total amount of the solvent of the nonaqueous electrolytic solution. By setting the range, it is possible to avoid a decrease in conductivity due to a decrease in dielectric constant of the nonaqueous electrolyte solution, and it is easy to achieve a good range of high-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the nonaqueous electrolyte battery. The upper limit is usually 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting the range, the oxidation/reduction resistance of the nonaqueous electrolytic solution can be improved, thereby contributing to improvement of stability at high-temperature storage. The content of the chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, and more preferably 25% by volume or more, based on the total amount of the solvent of the nonaqueous electrolytic solution. In addition, the volume ratio is usually 90% or less, preferably 85% or less, and more preferably 80% or less. By setting the content of the chain carbonate in the above range, the viscosity of the nonaqueous electrolytic solution can be easily set to an appropriate range, and the decrease in the ionic conductivity can be suppressed, thereby contributing to the improvement in the output characteristics of the nonaqueous electrolyte battery. When two or more kinds of chain carbonates are used in combination, the total amount of the chain carbonates may be set to satisfy the above range.
In some embodiments, it may also be preferable to use a chain carbonate having a fluorine atom (hereinafter simply referred to as "fluorinated chain carbonate"). The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, preferably 4 or less. In the case where the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms may be bonded to the same carbon or may be bonded to different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, and fluorinated diethyl carbonate derivatives.
The carboxylic acid ester solvent includes a cyclic carboxylic acid ester and/or a chain carbonate. Examples of the cyclic carboxylic acid ester include: one or more of gamma-butyrolactone, gamma-valerolactone and delta-valerolactone. Examples of the chain carbonate include, for example: one or more of Methyl Acetate (MA), ethyl Acetate (EA), propyl acetate (EP), butyl acetate, propyl Propionate (PP) and butyl propionate.
In some embodiments, the sulfone-based solvent includes cyclic sulfones and chain sulfones, preferably compounds having generally 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms in the case of cyclic sulfones, and generally 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms in the case of chain sulfones. The amount of the sulfone-based solvent to be added is not particularly limited, and is arbitrary within a range that does not significantly impair the effect of the lithium ion battery of the present invention, and is usually 0.3% or more by volume, preferably 0.5% or more by volume, more preferably 1% or more by volume, and is usually 40% or less by volume, preferably 35% or less by volume, more preferably 30% or less by volume, based on the total amount of the solvent of the nonaqueous electrolyte. When two or more sulfone solvents are used in combination, the total amount of sulfone solvents may be set to satisfy the above range. When the amount of the sulfone-based solvent added is within the above range, an electrolyte solution excellent in high-temperature storage stability tends to be obtained.
In a preferred embodiment, the solvent is a mixture of cyclic carbonates and chain carbonates.
In some embodiments, the nonaqueous electrolyte further comprises a lithium salt comprising LiPF 6 、LiPO 2 F 2 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiN(SO 2 CF 3 ) 2 、LiN(SO 2 C 2 F 5 ) 2 、LiC(SO 2 CF 3 ) 3 、LiN(SO 2 F) 2 、LiClO 4 、LiAlCl 4 、LiCF 3 SO 3 One or more of lower aliphatic carboxylic acid lithium salts.
In a preferred embodiment, the lithium salt comprises LiPF 6 And an auxiliary lithium salt, the auxiliary lithium salt comprising LiPO 2 F 2 、LiSbF 6 、LiAsF 6 、LiN(SO 2 CF 3 ) 2 、LiN(SO 2 C 2 F 5 ) 2 、LiC(SO 2 CF 3 ) 3 、LiN(SO 2 F) 2 、LiClO 4 、LiAlCl 4 、LiCF 3 SO 3 One or more of lower aliphatic carboxylic acid lithium salts.
Is satisfied thatUnder the above conditions, adding LiPF to the nonaqueous electrolyte 6 The thermal shock resistance of the battery can be further improved by adding the main lithium salt and the auxiliary lithium salt, and it is presumed that the compound represented by the formula II contained in the positive electrode is slightly dissolved in the nonaqueous electrolyte solution, and the combination of the compound and the lithium salt has the effect of improving the stability of the nonaqueous electrolyte solution and preventing the decomposition and gas generation of the nonaqueous electrolyte solution.
In some embodiments, the concentration of the lithium salt in the nonaqueous electrolytic solution is 0.1mol/L to 8mol/L. In a preferred embodiment, the concentration of the electrolyte salt in the nonaqueous electrolytic solution is 0.5mol/L to 4mol/L. Specifically, the concentration of the lithium salt may be 0.5mol/L, 1mol/L, 1.5mol/L, 2mol/L, 2.5mol/L, 3mol/L, 3.5mol/L or 4mol/L.
In some embodiments, in the nonaqueous electrolytic solution, the LiPF 6 The mass percentage of the auxiliary lithium salt is 5-20%, and the mass percentage of the auxiliary lithium salt is 0.05-5%.
In some embodiments, the nonaqueous electrolyte further includes a second additive further including at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, an unsaturated phosphate compound, a borate compound, and a nitrile compound;
preferably, the second additive is added in an amount of 0.01% to 30% based on 100% of the total mass of the nonaqueous electrolytic solution.
Preferably, the cyclic sulfate compound is selected from the group consisting of vinyl sulfate, vinyl 4-methylsulfate, propylene sulfate, and, At least one of vinyl methyl sulfate;
the sultone compound is selected from 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propylene sultone orAt least one of (a) and (b);
the cyclic carbonate compound is at least one selected from ethylene carbonate, fluoroethylene carbonate or a compound shown in a structural formula III,
in the structural formula III, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group;
the unsaturated phosphate compound is at least one compound shown in a structural formula IV:
in the formula IV, R 31 、R 32 、R 33 Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si (C) m H 2m+1 ) 3 M is a natural number of 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group;
in a preferred embodiment, the unsaturated phosphate compound may be at least one of tripropylethyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2, 2-trifluoroethyl phosphate, dipropargyl-3, 3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2, 2-trifluoroethyl phosphate, diallyl-3, 3-trifluoropropyl phosphate, diallyl hexafluoroisopropyl phosphate;
the borate compound is at least one selected from tri (trimethylsilane) borate and tri (triethylsilane) borate;
The nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether, hexanedinitrile, adiponitrile, pimelic dinitrile, suberonitrile, nonyldinitrile and decyldinitrile.
In other embodiments, the second additive may further comprise other additives that improve battery performance: for example, additives that enhance the safety performance of the battery, specifically flame retardant additives such as fluorophosphate and cyclophosphazene, or overcharge-preventing additives such as t-amyl benzene and t-butyl benzene.
In general, the amount of any one of the optional substances in the second additive to be added to the nonaqueous electrolytic solution is 10% or less, preferably 0.1 to 5%, and more preferably 0.1 to 2%, unless otherwise specified. Specifically, the amount of any optional substance in the second additive may be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8.5%, 9%, 9.5%, 10%.
In some embodiments, when the second additive is selected from fluoroethylene carbonate, the fluoroethylene carbonate is added in an amount of 0.05% to 30% based on 100% of the total mass of the nonaqueous electrolytic solution.
In some embodiments, the negative electrode sheet includes a negative electrode material layer including a negative electrode active material selected from at least one of a silicon-based negative electrode, a carbon-based negative electrode, a lithium-based negative electrode, and a tin-based negative electrode.
Wherein the silicon-based negative electrode comprises one or more of a silicon material, a silicon oxide, a silicon-carbon composite material and a silicon alloy material; the carbon-based negative electrode comprises one or more of graphite, hard carbon, soft carbon, graphene and mesophase carbon microspheres; one or more of the lithium-based negative electrode metallic lithium or lithium alloy. The lithium alloy can be at least one of lithium silicon alloy, lithium sodium alloy, lithium potassium alloy, lithium aluminum alloy, lithium tin alloy and lithium indium alloy. The tin-based negative electrode comprises one or more of tin, tin carbon, tin oxygen and tin metal compounds.
In some embodiments, the negative electrode material layer further comprises a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.
The selectable ranges of the negative electrode binder and the negative electrode conductive agent are the same as those of the positive electrode binder and the positive electrode conductive agent, respectively, and are not described in detail herein.
In some embodiments, the negative electrode tab further includes a negative electrode current collector, and the negative electrode material layer is formed on a surface of the negative electrode current collector.
The negative current collector is selected from a metal material that is conductive to electrons, preferably, the negative current collector includes one or more of Al, ni, tin, copper, stainless steel, and in a more preferred embodiment, the negative current collector is selected from copper foil.
In some embodiments, the lithium ion battery further comprises a separator, wherein the separator is positioned between the positive electrode sheet and the negative electrode sheet.
The separator may be an existing conventional separator, and may be a polymer separator, a non-woven fabric, etc., including but not limited to a single-layer PP (polypropylene), a single-layer PE (polyethylene), a double-layer PP/PE, a double-layer PP/PP, a triple-layer PP/PE/PP, etc.
The invention is further illustrated by the following examples.
The compounds referred to in the following examples and comparative examples are shown in table 1 below:
TABLE 1
Table 2 examples and comparative examples designs of parameters
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Example 1
The embodiment is used for explaining the lithium ion battery and the preparation method thereof, and comprises the following operation steps:
1) Preparation of positive plate
Step 1: PVDF as a binder and a compound represented by formula II shown in Table 2 were added to NMP solvent, and stirred well to obtain PVDF dope to which the compound represented by formula II was added.
Step 2: and adding a conductive agent (super P+CNT) into the PVDF glue solution, and fully and uniformly stirring.
Step 3: the positive electrode active materials shown in table 2 were continuously added, and sufficiently and uniformly stirred to finally obtain the desired positive electrode slurry.
Step 4: and uniformly coating the prepared positive electrode slurry on a positive electrode current collector (such as aluminum foil), and drying, rolling, die cutting or slitting to obtain the positive electrode plate.
2) Preparation of negative electrode sheet
Step 1: the materials are weighed according to the proportion of graphite (Shanghai fir, FSN-1) conductive carbon (super P) sodium carboxymethylcellulose (CMC) Styrene Butadiene Rubber (SBR) =96.3:1.0:1.2:1.5 (mass ratio) negative electrode plate.
Step 2: firstly, CMC is added into pure water according to the solid content of 1.5 percent, and the mixture is fully and uniformly stirred (for example, the stirring time is 120 min) to prepare transparent CMC glue solution.
Step 3: and adding conductive carbon (super P) into the CMC glue solution, and fully and uniformly stirring (for example, stirring for 90 min) to prepare the conductive glue.
Step 4: and continuously adding graphite, and fully and uniformly stirring to finally obtain the required negative electrode slurry.
Step 5: and uniformly coating the prepared negative electrode slurry on a copper foil, and drying, rolling, die cutting or slitting to obtain a negative electrode plate.
3) Preparation of nonaqueous electrolyte
Mixing Ethylene Carbonate (EC), diethyl carbonate (DEC) and ethylmethyl carbonate (EMC) at a mass ratio ec:dec:emc=1:1:1, adding additives in mass percentages as shown in table 2, and then adding lithium hexafluorophosphate (LiPF 6 ) To a molar concentration of 1mol/L.
4) Lithium ion cell preparation
And assembling the prepared positive plate and the prepared negative plate into a laminated soft-package battery cell.
5) Injection and formation of battery cell
In a glove box with the dew point controlled below-40 ℃, the prepared electrolyte is injected into a battery cell, and the battery cell is subjected to vacuum packaging and is kept for 24 hours. Then the first charge is conventionally formed by the following steps: and (3) carrying out constant current charging at 0.05C for 180min, carrying out constant current charging at 0.2C to 4.4V, carrying out secondary vacuum sealing, then further carrying out constant current charging at 0.2C to 4.85V, and carrying out constant current discharging at 0.2C to 3.4V after standing for 24h at normal temperature.
Examples 2 to 26
Examples 2 to 26 illustrate the lithium ion battery and the method of manufacturing the same disclosed in the present invention, including most of the operation steps in example 1, which are different in that:
the positive electrode sheet components and electrolyte addition components shown in table 2 were used.
Comparative examples 1 to 22
Comparative examples 1 to 22 are for comparative illustration of the lithium ion battery and the method for preparing the same disclosed in the present invention, including most of the operation steps in example 1, which are different in that:
The positive electrode sheet components and electrolyte addition components shown in table 2 were used.
Performance testing
The lithium ion battery prepared by the method is subjected to the following performance test:
and (3) testing normal temperature cycle performance:
the lithium ion batteries prepared in the examples and the comparative examples were charged at a 1C rate and discharged at a 1C rate at 25℃and subjected to a full charge discharge cycle test in a charge/discharge cutoff voltage of 3.4V to 4.85V until the capacity of the lithium ion battery was attenuated to 80% of the initial capacity, and the number of cycles was recorded.
And (3) dissolution test of positive manganese element:
the battery having the above-mentioned normal temperature cycle capacity attenuated to 80% of the initial capacity was discharged to 0% soc at 0.1C rate, and then the negative electrode was taken out by disassembling the battery, and the negative electrode taken out was immersed in DMC, thereby washing the negative electrode. Then, the negative electrode material layer on the negative electrode current collector was scraped off, thereby obtaining a detection sample. Then, the test sample was immersed in an aqueous nitric acid solution for 30 minutes. Thereby, the element as the detection target is dissolved (eluted) in the acid solution. The solution was detected by inductively coupled plasma emission spectrometry (ICP-OES) to obtain the content of eluted manganese element (ppm) as the positive electrode.
(1) The test results obtained in examples 1 to 16 and comparative examples 1 to 5 and 11 to 22 are filled in Table 3.
TABLE 3 Table 3
According to the test results of examples 1 to 16 and comparative examples 1 to 5 and 11 to 22, when the dissolution effect of manganese ions in the positive electrode material and the decomposition reaction direction of the nonaqueous electrolyte are inhibited, the mass percentage a of the compound shown in formula II in the positive electrode material layer and the mass percentage b of the boron-containing lithium salt in the nonaqueous electrolyte are inhibited, and the capacitance m of the unit area of the positive electrode material layer have the mutual correlation effect, particularly, when the mass percentage a of the compound shown in formula II in the positive electrode material layer, the mass percentage b of the boron-containing lithium salt in the nonaqueous electrolyte and the capacitance m of the unit area of the positive electrode material layer meet the limit of the relation 0.1 (a+b) m < 5), the structural stability and the oxidation resistance of the high-voltage nickel lithium manganate material can be maintained, the decomposition reaction of the electrolyte is obviously inhibited, and the cycle performance of the battery is improved, and the fact that the compound shown in formula II is decomposed on the surface of the nickel lithium manganate material to generate a layer which can resist electric decomposition, chemical corrosion or high-temperature conditions is supposed, and the functional boron-containing lithium salt shown in the formula II is improved, and the surface of the lithium manganate material can be modified in a mode, and the surface of the lithium manganate material can be further adjusted by the surface of the electrolyte material is better than the lithium manganate.
As shown by the test results of examples 1 to 16, as the capacitance m of the unit area of the positive electrode material layer increases, the initial capacity of the lithium ion battery is increased, but the cycle number thereof is gradually decreased, which means that too high a capacitance m of the unit area of the positive electrode material layer is unfavorable for improving the cycle performance of the battery, and too low a capacitance m is unfavorable for improving the energy density of the battery; and with the improvement of the content of the compound shown in the formula II in the positive electrode material layer, the adverse effect on the battery cycle performance due to the improvement of the capacitance m of the unit area of the positive electrode material layer can be effectively inhibited, and with the improvement of the content of the boron-containing lithium salt in the nonaqueous electrolyte, the dissolution effect of the interfacial film obtained by decomposing the compound shown in the formula II on manganese ions can be enhanced, however, it is required that the excessive boron-containing lithium salt brings about corresponding side effects, such as the improvement of impedance, resulting in the reduction of the battery cycle performance, so that when the mass percentage a of the compound shown in the formula II in the positive electrode material layer, the mass percentage b of the boron-containing lithium salt in the nonaqueous electrolyte and the capacitance m of the unit area of the positive electrode material layer are in the above relational expression range, the lithium ion battery with better mutual promotion and mutual restriction effects can be obtained.
From comparison of the test results of example 1 and comparative examples 1 to 4, it is understood that the addition of the compound represented by formula II is necessary for the present battery system, and that it is difficult to obtain an interfacial film having good composite properties on the surface of the positive electrode active material by only adding the boron-containing lithium salt in the absence of the compound represented by formula II, resulting in a decrease in the cycle performance of the battery and a severe dissolution of the positive electrode manganese ions.
As is clear from comparison of the test results of example 1 and comparative example 5, when the compound represented by formula II was added to the nonaqueous electrolytic solution, the performance improvement for the battery was far less than that when the compound represented by formula II was added to the positive electrode material layer, probably because the viscosity of the compound represented by formula II was large, the conductivity was low, and the addition to the electrolytic solution affected the capacity, internal resistance, cycle and the like of the battery.
As is clear from the test results of comparative examples 17 to 22, even if the values a, b and m satisfy the parameter ranges, the excessive or insufficient values of (a+b) and m result in the degradation of the battery cycle performance and the elution of manganese ions, which means that the mass percentage a of the compound shown in formula II in the positive electrode material layer, the mass percentage b of the boron-containing lithium salt in the nonaqueous electrolyte, and the capacitance m per unit area of the positive electrode material layer affect each other in terms of improving the battery cycle performance, and if and only if the three reach a better balance state, the electrochemical performance of the battery can be improved significantly. Meanwhile, as is clear from the test results of comparative examples 11 to 16, when one of the values of a, b and m exceeds the limit range, even if the relational expression can be satisfied: the requirement that (a+b) m is less than or equal to 0.1 and less than or equal to 5 is met, the cycle number of the battery is also poor, and the manganese ion in the lithium nickel manganese oxide material is seriously dissolved out, which indicates that when the mass percent a of the compound shown in the formula II in the positive electrode material layer, the mass percent b of the boron-containing lithium salt in the nonaqueous electrolyte and the capacitance m of the unit area of the positive electrode material layer are too high or too low, the formation of an interface film on the surface of the positive electrode and the negative electrode is influenced, and the stability of the interface film is reduced.
(2) The test results obtained in examples 1, 17 to 20 and comparative examples 6 to 10 are filled in Table 4.
TABLE 4 Table 4
Examples/comparative examples Initial capacity mAh of battery Cycle number of 25 DEG C Mn ion content/ppm
Example 1 1170 856 45
Example 17 1179 871 30
Example 18 1177 867 34
Example 19 1174 863 38
Example 20 1172 860 42
Comparative example 6 1157 611 303
Comparative example 7 1165 734 155
Comparative example 8 1163 729 161
Comparative example 9 1161 724 166
Comparative example 10 1159 720 171
As is clear from the test results of examples 1, 17 to 20 and comparative examples 6 to 10, although the compound represented by formula II was added to the positive electrode material layer, the additives DTD (vinyl sulfate), PS (1, 3-propane sultone), liPO were added to the nonaqueous electrolytic solution 2 F 2 When (lithium difluorophosphate) or FEC (fluoroethylene carbonate) is used for replacing boron-containing lithium salt, the improvement degree of the battery is far less than that of adding the boron-containing lithium salt into electrolyte, and it is speculated that under a high-voltage nickel lithium manganate system, the boron-containing lithium salt is more favorable for film forming reaction with a compound shown as a formula II on the surface of a material, and the formed interface film is stronger and stable, so that the protection effect on the cathode material is better, and the lithium nickel manganate battery system is causedThe cycle improvement of (C) was greater, and it was also seen that DTD (vinyl sulfate), PS (1, 3-propane sultone), liPO 2 F 2 The (lithium difluorophosphate) or FEC (fluoroethylene carbonate) has certain performance improvement effect on the battery system, but the improvement effect is not obvious as that of the compound shown in the formula II and the boron-containing lithium salt.
(3) The test results obtained in examples 1 and 21 to 26 are shown in Table 5.
TABLE 5
Examples/comparative examples Initial capacity mAh of battery Cycle number of 25 DEG C Mn ion content/ppm
Example 1 1170 856 45
Example 21 1167 854 47
Example 22 1162 850 51
Example 23 1165 852 48
Example 24 1159 846 54
Example 25 1150 868 44
Example 26 1179 834 68
From the test results of examples 1 and 21 to 24, it is known that, for the different compounds shown in formula II, when the mass percentage content a of the compound shown in formula II in the positive electrode material layer, the mass percentage content b of the boron-containing lithium salt in the nonaqueous electrolyte solution, and the capacitance m of the positive electrode material layer per unit area satisfy the preset relationship of 0.1 to less than or equal to (a+b) m to less than or equal to 5, the functions are similar, and the improvement effect on the battery energy density and the cycle performance of the battery is provided, which indicates that the relationship provided by the invention is applicable to the different compounds shown in formula II.
Meanwhile, as shown by the test results of examples 1, 25 and 26, other nickel manganate materials (such as x= 0.3,0.8) are adopted as the positive electrode active material, when the mass percentage content a of the compound shown in the formula II in the positive electrode material layer, the mass percentage content b of the boron-containing lithium salt in the nonaqueous electrolyte and the capacitance m of the unit area of the positive electrode material layer satisfy the preset relationship of 0.1 (a+b) ×m < 5, the battery has better cycle performance and initial capacity as well, and as the nickel content in the nickel manganate material is increased, the energy density of the battery is increased, but the cycle performance is reduced, and the dissolution of manganese ions is increased.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims (14)

1. The lithium ion battery is characterized by comprising a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, and the positive electrode material layer comprises a lithium nickel manganese oxide material shown in a formula I and a compound shown in a formula II;
LiNi x Mn 2-x O 4 i is a kind of
Wherein x is more than 0 and less than 2;
wherein R is 1 、R 2 、R 3 Each independently selected from alkyl of 1 to 5 carbon atoms, fluoroalkyl of 1 to 5 carbon atoms, ether of 1 to 5 carbon atoms, fluoroether of 1 to 5 carbon atoms, unsaturated hydrocarbon of 2 to 5 carbon atoms, and R 1 、R 2 、R 3 At least one of which is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;
the nonaqueous electrolyte includes a nonaqueous organic solvent, an electrolyte salt, and a first additive including a boron-containing lithium salt;
the lithium ion battery meets the following conditions:
0.1≤(a+b)*m≤5；
and a is more than or equal to 0.005 and less than or equal to 1, b is more than or equal to 0.01 and less than or equal to 3, and m is more than or equal to 1 and less than or equal to 3;
wherein a is the mass percentage of the compound shown in the formula II in the positive electrode material layer, and the unit is;
b is the mass percentage content of boron-containing lithium salt in the nonaqueous electrolyte, and the unit is;
m is capacitance per unit area of the positive electrode material layer, and the unit ismAh/cm 2 。
2. The lithium ion battery of claim 1, wherein the lithium ion battery meets the following conditions:
0.5≤(a+b)*m≤2。
3. the lithium ion battery according to claim 1, wherein the mass percentage content a of the compound shown in formula II in the positive electrode material layer is 0.05% -0.3%.
4. The lithium ion battery according to claim 1, wherein the mass percentage content b of the boron-containing lithium salt in the nonaqueous electrolyte is 0.05% -1%.
5. The lithium ion battery according to claim 1, wherein the capacitance m per unit area of the positive electrode material layer is 1.6 to 2.5mAh/cm 2 。
6. The lithium ion battery of claim 1, wherein the lithium nickel manganese oxide material of formula I is selected from LiNi 0.1 Mn 1.9 O 4 、LiNi 0.2 Mn 1.8 O 4 、LiNi 0.5 Mn 1.5 O 4 、LiNi 0.8 Mn 1.2 O 4 、LiNi 1.0 Mn 1.0 O 4 、LiNi 1.2 Mn 0.8 O 4 、LiNi 1.5 Mn 0.5 O 4 Or LiNi 1.8 Mn 0.2 O 4 At least one of them.
7. The lithium ion battery of claim 1, wherein the lithium nickel manganese oxide material shown in formula I in the positive electrode material layer is 90.0-99% by mass.
8. The lithium ion battery according to claim 1, wherein the solution obtained after the ultrasonic oscillation of the positive electrode in the solvent is analyzed by a liquid chromatography-mass spectrometer (LC-MS), and a characteristic peak appears in a region with a retention time of 6.5min to 7.5 min.
9. The lithium ion battery of claim 1, wherein the boron-containing lithium salt is selected from one or more of lithium bisoxalato borate, lithium difluorooxalato borate, and lithium tetrafluoroborate.
10. The lithium ion battery of claim 1, wherein the alkyl group of 1 to 5 carbon atoms is selected from the group consisting of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, and neopentyl; a fluoroalkyl group having 1 to 5 carbon atoms selected from the group consisting of a group in which one or more hydrogen elements in the alkyl group having 1 to 5 carbon atoms are substituted with a fluorine element;
the unsaturated hydrocarbon group of 2 to 5 carbon atoms is selected from vinyl, propenyl, allyl, butenyl, pentenyl, methylvinyl, methallyl, ethynyl, propynyl, propargyl, butynyl or pentynyl;
the ether group with 1-5 carbon atoms is selected from methyl ether, diethyl ether, methylethyl ether, propyl ether, methylpropyl ether or ethylpropyl ether;
the fluoroether group with 1-5 carbon atoms is selected from fluoromethyl ether, fluoroethyl ether, fluoromethyl ethyl ether, fluoropropyl ether, fluoromethyl propyl ether or fluoroethyl propyl ether.
11. The lithium ion battery of claim 1, wherein the compound of formula II is selected from at least one of tripropylethyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, dipropargyl methoxy methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2, 2-trifluoroethyl phosphate, dipropargyl 3, 3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, dipropargyl methyl ether phosphate, dipropargyl fluoromethyl ether phosphate, 2-trifluoroethyl diallyl phosphate, diallyl 3, 3-trifluoropropyl phosphate, or diallyl hexafluoroisopropyl phosphate.
12. The lithium ion battery of claim 1, wherein the nonaqueous electrolyte further comprises a second additive, the second additive further comprising at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, an unsaturated phosphate compound, a borate compound, and a nitrile compound.
13. The lithium ion battery according to claim 12, wherein the second additive is added in an amount of 0.01% to 30% based on 100% of the total mass of the nonaqueous electrolytic solution.
14. The lithium ion battery of claim 12, wherein the cyclic sulfate compound is selected from the group consisting of vinyl sulfate, vinyl 4-methylsulfate, propylene sulfate, vinyl methylsulfate,At least one of (a) and (b);
the sultone compound is selected from 1, 3-propane sultone, 1, 4-butane sultone, 1, 3-propylene sultone orAt least one of (a) and (b);
the cyclic carbonate compound is at least one selected from ethylene carbonate, fluoroethylene carbonate or a compound shown in a structural formula III,
the structure typeIII, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each independently selected from one of a hydrogen atom, a halogen atom, a C1-C5 group;
the unsaturated phosphate compound is at least one compound shown in a structural formula IV:
in the formula IV, R 31 、R 32 、R 33 Each independently selected from the group consisting of C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si (C) m H 2m+1 ) 3 M is a natural number of 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group;
the borate compound is at least one selected from tri (trimethylsilane) borate and tri (triethylsilane) borate;
the nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis (propionitrile) ether, hexanedinitrile, adiponitrile, pimelic dinitrile, suberonitrile, nonyldinitrile and decyldinitrile.
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